A thermometer implant—especially useful in medical diagnostic and therapeutic procedures—comprises a thermometer body containing a fluid which expands and contracts to a fluid length which indicates a target temperature at a target time and which is located in a body from where the fluid length is not visible at the target time, with the fluid length at the target time being measured outside the body.
When, for example, a cancerous tumor is treated by hyperthermia or cryotherapy it is very important to control the temperature in the tumor as well as the temperature in healthy tissue. Since existing temperature sensors are not adequate to the task, workers have long been seeking new ways to measure the temperature for such cases.
An implanted reflector which reflects a microwave signal as a function of temperature is shown by Nowogrodzki in U.S. Pat. No. 4,138,998. An implanted element which has temperature dependent nuclear magnetic resonance properties is shown by Taicher in U.S. Pat. No. 5,109,853.
The invention shown here is based on the discovery that small, expanding fluid thermometers can be made with properties which solve this long outstanding problem.